1. Field of the Invention
The present invention relates to a method of detecting the degree of unbalance of a work and/or tool to be mounted on a machine tool and a vibration state corresponding to the number of rotations of the work and/or tool at the stage of operation.
2. Description of the Related Art
The positions of the rotational centers of a machine tool, a tool which performs a rotational work, and a work which is to be cut, formed or so by the tool may not match with the positions of the centers of gravity thereof, and it is not rarely the case that there is a minute distance-oriented deviation (difference) between the position of the rotational center and the position of the center of gravity.
Given that m is the mass of a work and/or tool, i.e., the mass of one or both of a work and a tool, r is a deviation-oriented distance between the rotational center and the center of gravity, centrifugal force given below acts on the work and/or tool by rotating at an angular velocity ω.f=mrω2 Due to the action of the centrifugal force, the real rotational centers of the work and/or tool and a machine tool having the work and/or tool go to a revolving state through an approximately circular motion each about the original position of the rotational center, as shown in FIG. 4. The revolving position of the real rotational center, when observed in a specific direction, shows a vibrating state.
The product of the mass m of the work and/or tool which influences the centrifugal force and the deviation-oriented distance r is defined as an unbalance amount. As apparent from the fundamental equation of the centrifugal force, a vibration state originating from unbalance is inevitably influenced by the unbalance amount mr and the rotational angular velocity ω.
Conventionally, a vibration state originating from unbalance of a machine tool which has a work and/or tool mounted thereon and is rotating, specifically, the vibration amplitude and/or vibration average speed of vibration, are detected by arranging a direct optical device or an electromagnetic-induction based detecting device at the machine tool, as described in Patent Document 1 (Japanese Unexamined Patent Publication No. H6-335801) and Patent Document 2 (Japanese PCT Patent Publication No. 2002-515832).
However, the conventional detecting methods essentially require that a detecting device and a circuit needed for the detection should be provided for each machine tool, and are therefore very disadvantageous from the viewpoints of the effective use of space and the economical cost.
In addition, when a sensor fails, the repair should be carried out for each machine tool, which is significantly troublesome.